Litterfall and leaf litter decomposition in a central African tropical mountain forest and Eucalyptus plantation

Abstract

Litterfall and leaf litter decomposition are important ecosystem processes that rarely have been quantified for African tropical forests. Litterfall was measured in the Nyungwe pristine forest (two years) (2°28′ S, 29°06′ E, 1915m a.s.l.) and a nearby Eucalyptus plantation (one year) (2°26′ S, 29°05 E, 1889m a.s.l.) in southwest Rwanda. To test the species effect and home field advantage on litter decomposition a 361-days experiment with single- and mixed-species leaf litter was carried out. The single-species litterbags were only installed in the pristine forest while the mixed-species litterbags were installed in both forest stands.Total litterfall amounted to 4.1±0.9 and 2.2±0.5tonha−1year−1 during the first year in the pristine forest and the Eucalyptus plantation, respectively; and 4.0±0.7tonha−1year−1 during the second year in the pristine forest. The contribution of leaf litter in the pristine forest was 69% in the first year and 75% in the second year. In the Eucalyptus plantation leaves contributed 79%. Litterfall peaked in the major (July–August) and minor (December–January) dry seasons and at the onset of the rainy season (September–October).In the pristine forest, the initial decay rate was highest for Cleistanthus polystachyus (CP) leaf litter (0.0330day−1), followed by the forest litter mixture (PE+CP+CG) (0.016day−1), and was lowest for Parinari excelsa (PE) (0.0094day−1). The final decay rate of CP, Carapa grandiflora (CG) and Eucalyptus litter mixture were similar (0.0014, 0.0013 and 0.0017day−1) and lower than the final decay rate of forest litter mixture (PE+CP+CG) (0.0021day−1). Decay rates could be related to litter properties such as nitrogen, lignin, Ca and polyphenol content. Mixing litter species caused a negative additive effect on the initial, while a positive additive effect was observed on the final decay rate in the pristine forest stand. Taken together, mixed-species litter showed increased mass loss compared to the expected weighed-based mass loss from the individual litter types in the mixture. Finally, stand type only affected the final decay rate of forest litter mixture (PE+CP+CG) that was lower in Eucalyptus than in pristine forest and is suggested to be caused by reduced forest floor humidity.